Oilfield tubulars are joined at their ends with threads. Typically, the male or pin thread on a tubular to be run into a wellbore is screwed to the female or box end of the tubular previously run into the wellbore. There are many thread designs available for normal well applications that don't involve expansion. However, when tubulars are expanded problems with known thread designs have occurred. In some cases the load flanks on the thread have spread apart allowing for leakage under pressure conditions. In other cases, the pin or box have failed from stress cracks due to the expansion. In yet other cases, the pin end of the connected joint shrank longitudinally due to the expansion and curled inwardly putting itself in the way of moving other tools or equipment through the expanded connection. In yet other circumstances, the combination of flank separation from expansion and applied pressure allowed fluid leakage to the outside of the connection past the box nose.
Various designs for expandable threaded oilfield tubular connections have been devised. Examples of some of the more contemporary designs can be seen in U.S. Pat. Nos. 6,409,175; 6,607,220 and 6,604,763.
The present invention seeks to address issues of connection failure by addressing issues relating to flank separation, pin end curling and fluid leakage past the box end to the exterior of the connection. A variety of embodiments are presented both in the form of a threaded pin and box and coupling type connections. Those skilled in the art will more readily appreciate the scope of the invention from the claims that appear below and the examples relating to the below described preferred embodiments.